FYI update for anyone following this thread...300 miles with the washers removed and no I'll effects. I'll even say it made zero feel difference one way or the other in the seat of the pants brake dyno. I'll leave it as is for now. Not gonna take it back apart just to reinstall those washers for no reason. I would argue there must be some gain (cooling, etc) with full floaters. Why else would every other performance disc be built that way.
As a side note, I got the idea to remove them trying to fix a pretty annoying brake shudder on the front. I'd never heard of this arond here. Some research ofer on multistrada.net revealed this is a pretty common problem on the bike. My efforts failed to cure my shudder and research seems to indicate new aftermarket rotors are the best, permanent solution. Anyone else facing this?